The present invention relates to switches and in particular to dual touch switch devices defining a pair of switches simultaneously closed in response to a single transverse touching force where at least one of the switches has a pressure responsive variable contact resistance.
Switching devices which are operable in response to the application of a transverse touching force are known. Frequently, however, it is desirable to perform several independent switching functions simultaneously upon the application of a single transverse touch force. For example, battery powered musical instruments have recently been developed wherein the keyboards consist of touch sensitive switches interconnected in resistive networks to thereby replace strings or keys utilized on conventional instruments. In such instruments it is desired to be able to generate two tones to form a two note chord by the application of a single transverse touching force. It is also desired to provide a switching device which will allow one of the tones to vary slightly in frequency while the other tone remains of a constant frequency. Such a variation in tone of one note in a dual note chord generates a novel and unusual sound effect in the musical instrument.
The present invention provides a dual switch touch sensitive structure where the dual switches are simultaneously actuated in response to a single touching force. Further, the present invention provides a semiconducting composition over the switch conductors (contacts) of at least one of the switches so that the resistance across the contact of that switch (contact resistance) varies inversely to the amount of force which is transversely applied to close the two switches. Thus, by rapidly increasing and decreasing the transverse force such as by rapidly moving the finger pressing downwardly on the switch, a verbrato or tremolo effect in one tone can be generated without varying the frequency of the tone in the other switch.